Decorative packaging, currency bills, labels, containers and many other objects used in different applications often display a repetitive pattern on metallized film, often formed as a polymer base layer and a metallized surface, such as copper or aluminum.
Some of these applications include a colored, metallic foil that is hot stamped, in place of ink, onto a substrate or melted onto a print substrate. For example, a hot stamp printing plate could be cast or engraved into a piece of metal and held by a heated fixture. Between the plate and substrate, a hot stamp “foil” (film) with a color or metal transfer ink coated in a thin layer is compressed onto the substrate to transfer the image. The printers could be flatbed platen units, rotary, units, or automatic web feed presses. It is also possible that holograms and/or diffractive images are added for enhanced security.
The use of enhanced security, hot stamp foils for authentication is becoming increasingly popular and is evident when one views many currency bills used in Europe and other countries. The enhanced security hot stamp foils often incorporate a hologram or other optical device, such as a diffraction grating or pattern or a kinegram. These devices allow enhanced protection and authenticity of various documents or plastic cards. Different substrates can be used, including PVC, coated papers, textured security or bank note papers, packaging films, textiles, thermosensitive papers, and other similar substrates.
It is also possible to use not only foil stamping methods, but also use embossing techniques with the substrates. For example, a metal plate with a specific image is created and pressed onto the substrate leaving behind an image. This process is different from foil stamping where the image is transferred rather than pressed. Sometimes a holographic “patch” can be created by embossing a hologram onto a hot stamped foil, or a narrow strip hologram can be made from hot stamped foil and applied to a document.
In one process, a printer hot stamps blank foil onto a document and creates a hologram by embossing a holographic image onto blank foil. The holograms can be embossed in-line using a blank foil or embossable substrate. One station could hot stamp chemicals onto the substrate and another station could emboss the image in foil. It is possible to surface coat a substrate with silver and chemicals to make holograms in-line such that hot stamping may not be required when using an embossable substrate.
In one prior art technique, the base layer of a hologram is created by hot stamping foil on a substrate using a rotating, heated, stamping cylinder and associated base roller. The substrate and foil pass between the cylinder and roller. The cylinder includes a raised pad to configure the holographic image. It is also possible to emboss by using a holographic printing plate (as a shim), and a rotating, heated, embossing cylinder and rubber-coated base roller. The applied foil with the substrate passes between the cylinder and roller and a raised pad, which is larger in size than the hot stamping pad, comes into contact with the foil to create the holographic image. Demetallization is often used to add further security and design with different levels of transparency.
Holograms are advantageously used because they combat counterfeiting and cannot be copied easily using a photocopier They are also difficult to scan digitally using computer equipment. Holograms allow validation, especially with hidden and embedded holographic images. It is also possible to use a “kinegram” image, such as formed from fine lines of different thicknesses and shapes on a metallized foil. As the angle of light changes, the image of the kinegram also changes, producing the effect of a moving picture that could enhance security.
In one common prior art demetallization system used with packaging, a web of metallized polymer film is printed with a repetitive pattern of etchant-resistant material that has been applied from a gravure roll, corresponding to the pattern desired to be produced on the metallized surface, typically an aluminized or copper surface. An aqueous sodium hydroxide (NaOH) solution having a concentration of up to 25% by weight (NaOH) is applied at a temperature from about 15° to about 100° C. across the web to contact and etch those areas of the metallized surface that are free of the etchant resistant material. This sodium hydroxide (NaOH) solution remains in contact with the web for about 0.1 to about 10 seconds, depending on the thickness and metal used in the metallized surface to permit the sodium hydroxide to dissolve the aluminum from those areas of the web not having the etchant-resistant material. The material then is washed to remove any excess etchant and etchant by-products.
Usually this type of system uses rollers that feed the web and dips the web into baths of liquid to effect the various steps. Some prior art improvements spray an etchant onto the film. Scrapers remove any etched material. These steps are usually followed by warm water sprays to wash any etchant from the film surface. Afterward, the washed film is hot air dried and chill-roll cooled.
In other prior art systems, a substrate film is printed with a pattern of water-based printing varnish having an etchant dissolved therein, which remains in contact with the metallized surface for a time sufficient to etch the pattern onto the metallized surface. Any excess etchant is washed from the film and dried.
Another improvement has a patterned laminate formed by printing an image of an etchant by gravure roller on a web and laminating the printed web with another web such that the image is sandwiched between the webs in contact with the metallized film. The etchant dissolves the metallized surface in the printed areas to provide a desired pattern. The resulting laminate may be used as a packaging material. Further prior art improvements include selectively demetallizing film in different areas to form a graduated optical density for decorative packaging or even security purposes.
One drawback of many prior art demetallization and pattern forming systems is the repetitive pattern that is consistently applied onto the metallized surface. In decorative packaging, this is acceptable. In other instances, such as the holographic metallized film where security is an issue, it is not acceptable. For example, it may be desirable to form a unique metallized pattern on currency bills or identifying labels instead of the prior art repetitive pattern that is typically applied to some currency bills, and areas of decorative packaging, labels, containers and other items.
It would be advantageous if a demetallization pattern could be uniquely applied by a system and method where a unique and item specific (such as currency bill specific) pattern could be applied individually to successively produced items, such as currency bills, labels, containers and similar items. This pattern could be a microscopic or macroscopic pattern.